Introduce intermediate build target for std.

This gives a place for common functions to be defined.

Change-Id: Ifac38e647ab1042a00d224a58e28a0e6807fa60c
diff --git a/src/dlog.c b/src/dlog.c
index 7874cab..cd1247b 100644
--- a/src/dlog.c
+++ b/src/dlog.c
@@ -20,9 +20,9 @@
 #include <stddef.h>
 
 #include "hf/arch/console.h"
-#include "hf/arch/std.h"
 
 #include "hf/spinlock.h"
+#include "hf/std.h"
 
 /* Keep macro alignment */
 /* clang-format off */